The present invention relates to intraocular lens systems or pseudophakos generally implanted after removal of the natural lens of an eye as a result of a cataract condition.
The problem of correcting impaired vision of an eye after cataract surgery has been tackled in various ways. The prior methods for remedying the blurred vision condition has included the use of eyeglasses which has the undesirable side effect of reducing peripheral vision and magnifying the visual image obtained by the eye being corrected. Cataract removal and correction of vision by eyeglasses produces double vision. Contact lenses offer a better solution, although not a perfect one, since magnification still occurs. Moreover, contact lenses are relatively difficult to wear by the majority of cataract post-operative patients.
Intraocular lens implantation solves the majority of the optical problems associated with natural lens removal. New problems arise with the insertion of pseudophakos, for example, the fixation, support, relocation, and sterilization of such artificial lens systems.
Most of the prior intraocular lenses have been positioned in the anterior chamber of the eye. The Ridley, Epstein, Binkhorst, and Copeland, lenses employ a variety of clips, loops, and stabilizers to fasten the lens to the iris portion of the eye. Reference is made to U.S. Pat. No. 3,906,551 issued to Otter and U.S. Pat. No. 3,922,728 to Krasnov as representative of artificial lens designs. Insertion of these lenses requires great surgical skill.
Other lenses have been placed in the posterior chamber of the eye, with less success because of the difficulty involved with such fixation and positioning. Ophthalmologic surgeons have favored anterior chamber intraocular lens placement because of the relative remoteness of the posterior chamber and of the additional skill needed to successfully perform posterior chamber implantations. In this regard, the U.S. Pat. No. 3,711,870 to Deitrick, and the U.S. Pat. No. 3,991,426 to Flom describe examples of posterior chamber lens devices.
An early development by Strampelli, in 1953, used the idea of placing an intraocular lens over the iris and into a wedging configuration between the periphery of the iris and the connecting sclera commonly referred to as the anterior chamber angle. This lens made extensive contact with the trabeculum and corneal endothelium, causing damage to both structures.
A later variation of the Strampelli lens was the Choyce family of lenses which reduced the radius thickness of the Strampelli lens. Less tissue reactive materials were used for the entire lens, also. However, the Choyce lenses have a tendency to dislocate inferiorly, which requires reentry into the eye for relocation of the lens or insertion of a new lens. To avoid a misfitting of the lens, the proper sized lens must be initially inserted. Measurement across the iris, from opposite points of the angle, vary from about 12 to 14 millimeters. Exact dimensioning across the anterior chamber of an eye cannot be determined accurately without entering the eye. Incision of the eye invariably releases aqueous humor causing the eye to change its exterior shape; becoming more oblate. Such deformation renders actual measurement unlikely, if not impossible. The method now used to measure the Choyce lens adds a fixed dimension to the horizontal exterior white-to-white length. The results are not completely accurate.
If an accurate measurement is to be obtained, the eye surgeon must have the proper sized lens immediately prepared for implantation. This procedure entails maintaining a complete line of intraocular lenses according to length and refractive power.
The current procedure for insertion of the Choyce lens requires filling the eye anterior chamber with balanced salt solution after insertion of a lens and later nudging or tapping the sclera perpendicular to the axis of the lens. If the lens is stable, the fit is proper, if the lens moves it is too short. The latter instance requires re-opening the chamber and inserting a longer lens. Post-operative patients are examined and made to blink to see if the lens is stable, again if the lens moves a new longer lens is required for re-insertion.